Spinning of acrylonitrile polymers



March 5, 1963 P. A. UCCI SPINNING 0F ACRYLONITRILE POLYMERS 3Sheets-Sheet 1 Filed Dec. 1, 1961 INVENTOR. POMPELI ANGELO UCCI 1% m.Tum

ATTORN EY March 5, 1963 P. A. UCCI 3,080,210

SPINNING 0F ACRYLONITRILEI POLYMERS ACRYLONITRILE POLYMER SPINNINGSOLUTION COAGULATING 8: STRETCHING IN A FIRST BATH WASHING L. J

STRETCHING IN A SECOND BATH WASHING L. J

RELAXING FINISHING l .l

DRYING I CRIMPING L J COLLECTING FIG. 3 INVENTOR. PQMPELIO ANGELO UCCIATTORNEY March 5, 1963 P. A. UCCI 3,080,210

SPINNING OF ACRYLONITRILE POLYMERS Filed Dec. 1, 1961 I 3 Sheets-Sheet 3FIG.'6.

INVENTOR. POMPELIO ANGELO UCCI im m. TM,

ATTORNEY fifizlfi Fatenteoi Mar. 5, 1963 3,830,210 SPINNTNG {HFAtCRYLONiTRHJE PQLYMEQS Pompeiio A. Ucci, Decatur, Ala, assignor, bymcsne assignments, to Monsanto (Zhemical Company, a corporation ofDeiaware Filed Dec. 1, 1961, No. 155,368 11 Claims. (Qt. 13-54) Thisinvention relates to the manufacture of improved shaped articles such asfibers, filaments, yarns and the like produced from acrylonitrilepolymers. More particularly,

this invention concerns said shaped articles characterized by having anormally lustrous appearance and possessing an optimum balance oflongitudinal and lateral properties and a process for producing same.

In view of the therrna instability of acrylonitrile polymers, filamentsof such polymers are formed by dissolving the polymers in a suitablesolvent and then removing the solvent from a flowing stream of thesolution to form filaments therefrom. Commercially, filaments ofacrylonitrile polymers are prepared either by the dry spinning processor by the wet spinning process, as is well known. The specific techniquechosen results in a compromise among yarn properties, the economicaspects of the technique involved, and other considerations. There areadvantages and disadvantages associated with the employment of eachprocess. For example, dry spinning has the advantage of considerablyhigher spinning speeds than those which can be attained with wetspinning. In addition, a greater percentage of solids can be toleratedin the spinning solution used in dry spinning as compared with thatwhich can be used in wet spinning since, inter alia, the solution isspun at relatively high temperatures. Unfortunately, the better solventsfor acrylonitrile polymers are not as volatile as would be desired foruse in the dry spinning process wherein the solvent is removed to agreat extent by evaporation into air or other suitable inert gas. Inview of the fact that at least 75 percent of the solvent is removed as agas in the dry spinning process, large amounts of heat must be appliedto the spinning solution, as well as to the extruded filaments, tofacilitate removal of such a quantity of solvent within a reasonabletime. The amounts of heat so required can afiect adversely theproperties of the produced filaments, particularly in regard to color.

When the solvent is extracted from an extruded stream of spinningsolution in a coagulating bath during wet spinning, solidification ofthe polymer in fiamentary form results. Normally, during coagulatingthere is an inward diffusion of coagulating bath liquid into thefilaments undergoing coagulation, as well as a corresponding ontwardmovement of solvent into the coagulating bath. The solvent and bathliquid can interchange in such a manner that the resulting filamentscontain many voids or cavities along their lengths which can be seenclearly with an optical phase microscope. Filaments containing thesevoids or unfilled spaces do not possess the requisite physicalproperties desired for some end uses. For example, such filamentsexhibit a delustered appearance, lower tenacity, and lower abrasionresistance than filaments not containing voids.

To overcome this physical weakness inherently formed in the filaments,positive aftertreatment steps during the processing of the filamentsnormally are taken. The tenacity of the filaments is improved greatly byvarious modes of stretching that molecularly orient the polymermolecules but which in addition tend to collapse these voids. Tocollapse fully these voids, the filaments may be dried at rather hightemperatures under tension, thereby forming a more dense filamentarystructure. The prior art has found that the tenacity of the filaments isbalance of properties.

satisfactory with such aftertreatment of the filaments. However,tenacity is primarily a longitudinal property of the filaments; andsatisfactory tenacity is not the full answer to the attainment offilaments having an optimum In many end uses the abrasion resistance andthe resistance to break upon being flexed (fiex life) are mostimportant. Such properties may be regarded as lateral properties asdistinguished from longitudinal properties. While drying under tensiongives the illusion of forming filaments without voids therein, the voidsmerely are crushed together. Although the crushed voids do not detractfrom the lon itudinal properties of the filaments to any significantextent, it has been found that lateral stresses cause the filaments tosplinter or break. In other words, filaments having voids which aremerely crushed together are laterally weak. The art has found that thelateral properties of the filaments can be improved substantially bysubjecting the filaments to an annealing operation. One such annealingprocedure includes a series of elevated and reduced pressure treatmentsapplied to the filaments. More specifically, annealing can beaccomplished by placing the acrylonitrile polymer filaments in a closedchamber, subjecting them to a high temperature and pressure in thepresence of wet steam and then evacuating the chamber. This treatingcycle is repeated as many times as needed. It will be appreciated thatthis annealing operation as just described is expensive and timeconsuming. Omitting the annealing step in the aftertreatment of the wetspun acrylic filaments results in a filament having a tendency tosplinter or fibrillate; and hence, the filaments have a low abrasionresistance. This tendency to fibrillate is minimized by annealing thefilaments. The improvement is thought to result from the interfacesurfaces of the collapsed voids being rendered less separable.

In addition to the possible presence of the voids whic are visible underan optical phase microscope and occur in filaments of acrylonitrilepolymers coagulated in an aqueous coagulating bath, electron microscopyhas shown the existence of a reticulate structure in the filamentsdisplaying a network of submicroscopic pores or interstitial spaces mostof which intercommunicate with each other. These pores in freshly spunfilaments, that is filaments which have been coagulated without havingbeen subjected to any aftertreatrnent producing a pronounced change inthe structure thereof, are quite observable under an electronmicroscope. The polymers comprising the filaments appear to take theform of a latticework of integrally joined strings. The polymer latticehas a pattern resembling that of a fine, extremely small meshwork,although the interstices are usually somewhat irregular in size andshape. The micropores present in filaments produced by ordinary wetspinning techniques as they leave the coagulating bath are more or lessspherical with the polymer lattice defining such interstitial spaces.The distances across these spaces are ordinarily about 250 A. to 3000 A.or greater. The frequency of occurrence of the micropores in thefilaments produced by ordinary Wet spinning techniques employing aqueouscoagulating baths can be estimated under an electron microscope and isusually around 3590 10 per gram of polymer. The presence of these poresis believed to explain the anomalously low density of normal filamentsas they leave the coagulating bath. At this point the apparent densityof the filaments produced by ordinary wet spinning techniques employingaqueous coagulating baths is usually about 0.4 to 0.5 gram per cubiccentimeter.

It will be appreciated that the voids that are visible under the opticalphase microscope are quite different from the micropores or interstitialspaces not visible under an optical phase microscope but readilyapparent under anelectron microscope. Hence, the term voids as usedherein signifies enclosed spaces or surface pits of the filaments whichare visible under an optical phase microscope and which do not containacrylonitrile polymer, whether or not the enclosed spaces contain afluid or are collapsed. The term micropore as used herein signifiesextremely diminutive enclosed spaces or surface pits of the filamentsthat are not visible under an optical phase microscope but visible underan electron microscope and that do not contain acrylonitrile polymer,whether or not the enclosed spaces contain a fluid or are collapsed.

When the freshly spun filaments are stretched, these micropores as wouldbe expected assume the geometric configuration of ellipsoids. Subsequentcollapsing of the porous structure of the filaments due to the presenceof these micropores can be accomplished by drying the filaments undertension at an elevated temperature. Annealing the filaments renders theinterstitial interface surfaces of the microp-ores less separable.Hence, annealing has been regarded as an important step in theattainment of acceptable lateral physical properties in the filaments.

It is an object of this invention to provide a process for producingfilaments and the like of acrylonitrile polymers that possess anadvantageous combination of lateral and longitudinal physical propertiesby modification of the conventional acrylonitrile polymer filamentforming processes. Other objects will become apparent from the followingdescription of the invention and the claims.

In general, these objects are accomplished in accordance with theinvention by continuously extruding a solution of an acrylonitrilepolymer through a desired number of orifices in a spinneret disposed inair or other inert gaseous medium and continuously directing thethusformed streams of the solution for a short distance through themedium, wherein only a very small amount of the solvent, if any, isevaporated into the ambient medium as a gas. The streams then are passedinto a liquid which is a precipitant for the polymer and an extractantfor the solvent, such as an aqueous coagulating bath. In the liquid baththe streams of polymer are coagulated into filaments by the substantialremoval therefrom of the solvent as a liquid. The solvent employed ispreferably N,N-dimethylacetamide, N,N-dimethylformarnide or the like;and the coagulating bath preferably is composed essentially of thesolvent and water. By employing such preferred solvent and bathcomposition while maintaining the bath temperature between the criticaltemperature range of C. to -40 (1., preferably between +10 C. and C.,thefilaments produced possess most advantageous physical properties anddiffer in structure from other acrylonitrile polymer filamentsheretofore known in the art. The extrusion rate of the polymer and thespeed of withdrawal of the filaments from the coagulating bath arecorrelated so that the filaments are subjected to a draw ratio usuallyof 0.8-2(). However, the filaments may be stretched at this point up tojust short of the point at which filamentary breakage occurs. Preferablythe draw ratio is between 0.5 and 5.0 times. Often higher draw ratiosare desired whereby to obtain higher spin-ning speeds. Draw ratio is aconvenient term for designating the attenuation or shrinkage that oftenoccurs during various steps in the production of man-made filaments.Draw ratio is the number resulting from the division of the speed ofwithdrawal by the speed of feed of the filaments between two givenpoints. In the production of wet-spun filaments draw ratio as applied tothe attenuation or shrinkage in the coagulating bath is the numberderived by dividing the measured length of filaments produced by thelength that should have been produced as calculated from the extrusionrate of polymer through the spinneret. Most of the attenuation, ifattenuation of the filaments is desired, occurs while the streams ofpolymer pass through the short air gap separating the face of thespinneret and the upper surface of the liquid in the coagulating bath,with little, if any, stretch taking place in the coagulating bath. Afterbeing passed through the coagulating bath for a sufiicient distance, thefilaments are continuously removed therefrom and directed through asecond bath. This bath is preferably composed of hot water whereinadditional solvent remaining in the coagulated filaments is removedtherefrom and a considerable stretch is imparted thereto to orient thepolymer molecules thereof. Following this operation, the filaments arepermitted to relax continuoutly under a low tension in a hot liquid orhot gaseous atmosphere and/or then continuously dried. The necessity ofthe continuous relaxation depends upon the spinning conditions employed.it has been found that when N,N-dimethylacetamide orN,N-dimethylformamide is employed as the solvent for the acrylonitrilepolymer and when an aqueous coagulating bath consisting primarily ofwater and solvent and maintained within the critical temperature rangeof +10 C. and 40 C. is used, the relaxing step unexpectedly can beomitted and yet produce filaments of textile grade. Moreover, it is notnecessary to dry the filaments under tension since the filaments aresubstantially free of voids and when dried at room temperature, whetherrelaxed or under tension, display densities corresponding to normallyproduced filaments dried under tension to insure that the voids andmicropores therein are collapsed.

To further understand the invention, reference will be made to theattached drawing that forms part of the present application.

In the drawing, FIGURE 1 is a side elevational view partly in sectionshowing schematically an apparatus arrangement of the type which can beused in carrying out the process of the present invention;

FIGURE 2 is a schematic view showing the produced filaments being driedby a different drying means;

FIGURE 3 is a flow sheet illustrating the manipulative steps used incarrying out the process of the invention;

FIGURE 4 is a reproduction of a p-hotomicrograph at a magnification ofabout 100 times of acrylonitrile polymer filaments of textile gradewhich give the appearance of smooth, glassy rods;

FIGURE 5 is a reproduction of a photomicrograph of greater magnificationof an acrylonitrile polymer filament that contains numerous voids alongthe length thereof;

FIGURE 6 is a reproduction of a photomicrograph of an acrylonitrilepolymer filament substantially free of voids; and

FIGURE 7 is a schematic view of a simple laboratory abrasion testingapparatus.

By acrylonitrile polymer is meant polyacrylonitrile, copolymers, andterpolymers of acrylonitrile, and blends of polyacrylonitrile andcopolymers of acrylonitrile with other polymerizable mono-olefinicmaterials, as well as blends of polyacrylonitrile and such copolymerswith small amounts of other polymeric materials, such as polystyrene. Ingeneral, a polymer made from a monomeric mixture of which acrylonitrileis at least 70 percent by weight of the polymerizable content is usefulin the practice of the present invention. Besides polyacrylonitrile,useful copolymers are those of or more percent of acrylonitrile and oneor more percent of other mono-olefinic monomers. Block and graftcopolymers of the same general type are within the purview of theinvention. Suitable other monomers include vinyl acetate, and othervinyl esters of monocarboxylic acids, vinylidene chloride, vinylchloride and other vinyl halides, dimethyl fumerate and other dialkylesters of fumaric acid, dirnethyl maleate and other dialkyl esters ofmaleic acid, methyl acrylate and other alkyl esters of acrylic acid,styrene and other vinylsu'bstituted aromatic hydrocarbons, methylmethacrylate and other alkyl esters of methacrylic acid,vinyl-substituted heterocyclic nitrogen ring compounds, such as thevinyl irnidazoles, etc., the alkyd-substituted vinylpyridines, vinylchloroacetate, allyl chloroacetate, methallyl chloroacetate,

allyl glycidyl ether, methallyl glycidyl ether, allyl glycidylphtlralate, and the corresponding esters of other aliphatic and aromaticdicarboxylic acids, glycidyl acrylate, glycidyl methacrylate, and othermono-olefinic monomers copolymerizable with acrylonitrile.

Many of the more readily available monomers for polymerization withacrylonitrile form copolymers which are not reactive with some dyestuffsand may therefore be impossible or difiicuit to dye by conventionaltechniques. Accordingly, these non-dyeable fiber-forming copolymers maybe blended with polymers or copolymers which are in themselves moredye-receptive by reason of their physical structure or by reason of thepresence of functional groups chemically reactive with the dyestuff,whereby the dyestuff is permanently bonded to the polymer in a man- Iner which lends resistance to removal thereof by the usual launderingand dry cleaning procedures. Suitable blending polymers may bepolyvinylpyridine, polymers of alkylsubstituted vinylpyridine, polymersof other vinyl-substituted N-heterocyclic compounds, the copolymers ofthe various vinyl-substituted N-heterocyclic compounds and othercopolymerizable monomers, particularly acrylonitrile.

Of particular utility are the blends formed of polyacrylonitrile or acopolymer of more than 90 percent acrylonitrile and up to percent vinylacetate, and a copolymer of vinylpyridine or an alkyl-substitutedvinylpyridine and acrylonitrile, the said acrylonitrile being present insubstantial proportions to provide heat and solvent resistance, and asubstantial proportion of the vinylpyridine or derivatives thereof torender the blend receptive to acid dyestuffs. Of particular utility arethe blends of copolymers of 90 to 98 percent acrylonitrile and 10 to 2percent vinyl acetate and sufficient copolymer of 10 to 70 percentacrylonitrile and 90 to percent vinylpyridine to produce a blendedcomposition with a total of 2 to 10 weight percent vinylpyridine.

The polymers just described may be prepared by any conventionalpolymerization procedure, such as mass polymerization methods, solutionpolymerization methods, or aqueous emulsion methods. The polymerizationis normally catalyzed by known catalysts and is carried out in equipmentgenerally used in the art. However, the preferred practice utilizessuspension polymerization wherein the polymer is prepared in finelydivided form for immediate use in the filament-forming operations. Thepreferred suspension polymerization involves batch procedures, whereinmonomers are charged with an aqueous medium containing the necessarycatalyst and dispersing agents. A more desirable method involves thesemi-continuous procedure in which the polymerization reactor containingthe aqueous medium is charged with the desired monomers graduallythroughout the course of the reaction. Entirely continuous methodsinvolving the gradual addition of monomers and the continuous withdrawalof polymer can also be employed.

The polymerization is catalyzed by means of a watersoluble peroxycompound, for example, the potassium, ammonium and other water-solublesalts of peroxy acids, sodium peroxide, hydrogen peroxide, sodiumperborate, the sodium salts of other peroXy acids, and otherwatersoluble compounds containing the peroxy group:

A wide variation in the quantity of peroXy compound is possible. Forexample, from 0.1 to 3.0 percent by weight of the polymerizable monomermay be used. The so-called redox catalyst system also may be used. Redoxagents are generally compounds in a lower valent state which are readilyoxidized to the higher valcnt state under the conditions of reaction.Through the use of this reductionoxidation system, it is possible toobtain polymerization to a substantial extent at lower temperatures thanotherwise would be required. Suitable redox agents are sulfur dioxide,the alkali metal and ammonium bisulfites,

and sodium formaldehyde sulfoxylate. The catalyst may be charged at theoutlet of the reaction, or it may be added continuously or in incrementsthrough out the reaction for the purpose of maintaining a more uniformconcentration of catalyst in the reaction mass. The latter method ispreferred because it tends to make the resultant polymer more uniform inregard to its chemical and physical properties.

Although the uniform distribution of the reactants throughout thereaction mass can be achieved by vigorous agitation, it is generallydesirable to promote the uniform distribution of reagents by using inertwetting agents, or emulsion stabilizers. Suitable reagents for thispurpose are the water-soluble salts of fatty acids, such as sodiumoleate and potassium stearate, mixtures of Water-soluble fatty acidsalts, such as common soaps prepared by the saponification of animal andvegetable oils, the amino soaps, such as salts of triethanolamine anddodecylmethylamine, salts of rosin acids and mixtures thereof, thewater-soluble salts of half esters of sulfonic acids and long chainaliphatic alcohols, sulfonated hydrocarbons, such as alkyl arylsulfonates, and any other of a wide variety of wetting agents, which arein general organic compounds containing both hydrophobic and hydrophilicradicals. The quantity of emulsifying agent will depend upon theparticular agent selected, the ratio of monomer to be used and theconditions of polymerization. In general, however, from 0.1 to 1.0weight percent based on the Weight of the monomers can be employed.

The emulsion polymerizations are preferably conducted in glass orglass-lined vessels provided with means for agitating the contentstherein. Generally, rotary stirring devices are the most effective meansof insuring the in timate contact of the reagents, but other methods maybe successfully employed, for example, by rocking or rotating thereactors. The polymerization equipment generally used is conventional inthe art and the adaptation of a particular type of apparatus to thereaction contemplated is within the province of one skilled in the art.

The optimum methods of polymerization for preparing fiber-formingacrylonitrile polymers involve the use of polymerization regulators toprevent the formation of polymer units of excessive molecular Weight.Suitable regulators are the alkyl and aryl mercaptans, carbontetrachloride, chloroform, dithioglycidol and alcohols. The regulatorsmay be used in amounts varying from 0.001 to two percent, based on theweight of the monomer to be polymerized.

The polymers from which the filaments are produced in accordance withthe present invention have specific viscosities within the range of 0.10to 0.40. The specific viscosity value, as employed herein, isrepresented by the formula:

Viscosity determinations of the polymer solutions and solvent are madeby allowing said solutions to flow by gravity at 25 C. through acapillary viscosity tube. In the determinations herein, a polymersolution containing 0.1 gram of the polymer dissolved in ml. of N,N-dimethylformamide was employed. The most effective polymers for thepreparation of filaments are those of uniform physical and chemicalproperties and of relatively high molecular Weight.

Referring now to FIGURE 1, a water coagulable solution comprising anacrylonitrile polymer and a solvent therefor is passed under pressurefrom a supply tank (not shown) through a conduit 10 and thence through acandle filter 11 wherein undissolved particles and foreign materials inthe solution are removed. Ordinarily, gear pumps are used to propel thesolution through the filter 11 and to meter same to the spinneretassembly 12. This assembly is suitably mounted and positioned such thatthe face 13 of the spinneret is horizontally disposed preferably along aplane substantially parallel to the upper surface of the coagulatingliquid 14 contained in an opentop spinning trough or bath 15. Thesolution may be extruded through a single orifice or a plurality oforifices in the spinneret to form a filament or a bundle of filaments 16as desired. The extruded streams of polymer are directed substantiallyvertically downward and under filament guide 17 disposed in said trough15. A second filament guide 18 is suitably positioned in said trough sothat the filaments directed thereunder will pass through the liquid 14for a predetermined distance sufficient to cause the solution tocoagulate as desired. Fresh liquid 14 is supplied to trough 15 throughpipe 24) (which may "be water or water containing a desirable quantityof solvent) and is withdrawn therefrom through pipe 21.

The coagulated filaments are withdrawn by employment of a positivelydriven roller 22 or other thread advancing means, the peripheral speedof which preferably is synchronized with the extrusion speed so that thefilaments during their travel between the spinneret and the rollers maybe attenuated, and if desired attenuated up to the point just short ofwhere filamentary breakage occurs. As indicated above, most of theattenuation will take place between the face of the spinneret and theupper surface of the coagulating bath. After passing around roller 22and an idler roll 23, the filaments are directed into a second spinningtrough 24 containing a liquid 25. Fresh liquid is supplied to trough 24through pipe 26 and is withdrawn therefrom through pipe 27. While it isquite possible to employ three or more liquid-containing troughs, onlytwo have been illustrated and described in the interest of simplicity.The filaments before emerging from the liquid in second trough 24 andbeing directed around a set of positively driven rollers identified bynumerals 28 and 36 are passed under guides 31 and 32. The peripheralspeed of rollers 28 and 3%) can be adjusted so that a predeterminedorientation stretch will be imparted to the filaments 16 during theirtravel in second trough 2%.

To roller 28 a washing liquid such as hot water is supplied from a sprayor shower head 33, the liquid being collected in a container or tray 34.It will be recognized that the Washing operation can be accomplished inmore than one stage of the process and by employment of other knownwashing means. After leaving rollers 28 and 30, the filaments aredirected through a liquid in a third trough 35 by being passed underguides 36 and 37. The liquid 38 in this trough is normally water at anelevated temperature. The filaments are withdrawn therefrom by means ofa driven roller 40 and associated idle roller 41 operated at aperipheral speed less than that of the peripheral speed of rollers 28and 3%] so that the filaments are permitted to relax substantiallycompletely and thereby to shrink during their travel in trough 35. Freshwater is supplied to trough 35 through an inlet pipe 42 and is withdrawnthrough an outlet pipe 43. It will be appreciated that other equivalentmeans may be used to permit the shrinking or relaxing of the filaments.For example, the filaments may be directed around a tapered roller orrollers and progressively led from the end having the largercircumference to the end having the smaller circumference, the rollersbeing immersed in a liquid or having a liquid applied thereto. Followingthe relaxing operation the filaments are passed through a finish bathliquid 44 contained in a vessel 45 and composed of a lubricant or likebeneficial treating agent. The filaments after being withdrawn fromliquid 44 are dried. As illustrated in FIGURE 1, the filaments arecontinuously directed around a pair of driven drying drums 46 and 47heated internally with steam or the like. Thereafter, the filaments aresubjected to additional operations such as crimping, cutting, and thenare collected in the form of staple fiber, continuous filament yarn, ortow.

In accordance with a second embodiment relative to the drying operationas illustrated in FIGURE 2, the filaments after being stretched andWashed are layed by means of a traversing piddler 48 or like guide meansonto a moving endless belt 50 (in a zig-zag pattern). This belt passesthrough a drying cabinet 51 in which hot air or other suitable dryinggas at an elevated temperature is directed onto the filaments therein.In this embodiment, it is seen that the filaments are continuously driedin a tension-free condition. An advantage of this embodiment is that thefilaments are permitted to relax and are dried; thus the relaxing andthe drying of the filaments are accomplished in one step. It should beunderstood that it is entirely possible to dry the filaments while notbeing tensioned by the employment of other drying means. For example,the filaments may be dried suitably by being conveyed by and suspendedin a stream of air.

FIGURE 3 is a fiow sheet illustrating a preferred arrangement of themanipulative steps used herein. As seen there, a prepared spinningsolution is extruded from a spinneret into air to form a bundle offilaments that are then coagulated. The filaments may be stretched asubstantial extent, if desired, betwen the spinneret and the means usedto withdraw them from the coagulating bath. From the coagulating baththe filaments so produced are passed through a second bath where theyare stretched and thence through a third bath in which the filaments arepermitted to relax. The filaments may be washed free or substantiallyfree of solvent either before or after they have been stretched in thesecond bath. After the relaxing operation, the filaments may be directedthrough a bath containing a suitable finish, if desired, and thereafterare dried by conventional means. Optionally, the filaments are crimped.Finally, the filaments are reduced to staple size and baled, oralternatively they are collected as continuous filaments by employmentof a suitable take-up device.

FEGURE 5 is a drawing prepared from a photomicrograph showing a view ofpart of a filament containing voids or cavities. Enclosed voids in thefilament also can be seen by observing a cross section of the filament.Due to the presence of the voids, the light rays impinging thereon arescattered, imparting a dull or subdued luster to the filament.

FIGURE 6 is a drawing prepared from a photomicrograph showing acorresponding view of part of a filament substantially free of voids orcavities. Due to the substantial absence of voids, the filament has alustrous appearance. The novel filaments of the present invention aresubstantially free of voids and hence have a normally lustrousappearance. However, when desired, delustrants, pigments, and the likecan be incorporated in the filaments to produce dull filaments. Themarked differences of the novel filaments herein and those heretoforeknown become more apparent when a comparison of the reticulatefilamentary structures is made at magnifications obtainable by the useof an electron microscope.

In general, the spinning solution can be prepared by heating andstirring a mixture of a finely divided acrylonitrile polymer of the typedescribed above with a suitable solvent until the polymer is dissolved.To some extent the selection of the solvent is influenced by theparticular polymer chosen. Certain materials such as N,N-dimethylformamide, butyrolactone, dimethyl sulfoxide,N,N-dimethylacetamide and the like are particularly suitable solvents.While ethyleue carbonate and the like, concentrated solutions of certainwater-soluble inorganic salts, such as zinc chloride, calcium chloride,lithium romide, cadmium bromide, sodium thiocyanate, etc. may beemployed in accordance with the broadest aspects of the invention, suchsolvents are not preferred for use in producing the novel filamentsherein or for use in the embodiment of the invention employing the lowtemperature coagulation bath of +10 C. to 40 C. The percentage ofpolymer based on the weight of the solution will depend upon theparticular polymer and solvent em- }ioyed, as well as upon thetemperature at which the polymer is spun. It is desirable to employ asolution containing a high percentage of polymer for obvious reasons.

An advantage of the present invention is the fact that spinningsolutions having much higher temperatures can be employed thanordinarily used in wet spinning. Hence, a greater percentage of polymerin the solution can be used with success. The spinning solution may bemaintained prior to and at extrusion at temperatures from about 20 to180 C. Room temperature is highly satisfactory from an operationalstandpoint. Ordinarily a solution containing at least 10 percentacrylonitrile polymer is desirable.

Since the viscosity of the acrylonitrile polymer solution variesdirectly with its temperature, advantage of employing the high spinningtemperatures permitted in the instant process may be taken with theresult that low extrusion pressures are required for a given percentageof polymer. Normally, the polymer solution temperature for successfulwet spinning should be closely correlated with the temperature of thecoagulating bath. In order to spin acrylonitrile polymer solution by theconventional wet spinning method, it is necessary to avoid elevatedcoagulating bath temperatures, since such temperatures substantiallyreduce the solvent extraction efficiency to a point Where it is notpossible or feasible to utilize the advantage of spinning a solutioncontaining a high percentage of polymer.

The spinneret used in accordance with the instant invention can be ofthe type ordinarily used in dry spinning operation. An importantvariable in any spinning process is the orifice diameter of thespinneret. From practical aspects it is of ten desirable to employ thelargest diameter consistent with good spinning. By increasing theorifice size the filtration of the spinning solution becomes lessimportant and the number of spinneret changes due to clogging thereof isreduced. In the present invention one may employ orifices havingrelatively large diameters due to the fact that the filaments may begiven a considerable attenuation immediately after extrusion of thespinning solution. This in practical terms means a reduction inoperating cost. Among other benefits derived by employing a largeorifice opening are the higher spinning speeds and the improvement inthe physical properties by the attenuation of the filaments that can beattained. In conventional wet spinning this is not possible because themaximum jet stretch that can be imparted to the freshly spun filamentsis usually less tha two times, and in most cases is less than one timedue to the anisotropic condition of normally wet spun filaments. On theother hand, it is possible to stretch the freshly spun filaments of thepresent invention to the extent of ashigh as times. That is to say, thatthe first take-up linear velocity may be up to 15 times the extrusionvelocity of the polymer. By disposing the spinneret above thecoagulating bath, it is possible to attain spinning speeds as high as100-1500 feet per minute using apparatus with which a maximum speed ofonly 75 to 150 feet per minute can be attained in normal wet spinning.Moreover, filament deniers below 1.0 can be spun readily withoutdifiiculty whereas 1.2 to 2.0 denier per filament is generally the leastthat can be spun in the ordinary wet spinning process. Another advantageof the present process is that a wide range of filament denier can bespun from a sin le spinneret. For example, filament deniers from 0.8 to22 and higher having satisfactory textile properties may be spun from asingle spinneret having an orifice diameter of 0.005 inch. This meansthat filaments having various deniers may be spun conveniently withoutshut down being required to change from production of one diameter toanother.

The distance that the spinneret is disposed above the coagulating bathmay be varied. Ordinarily, the spinn eret is positioned so that its faceis between A; and 1 /2 inches above the bath. However, one can increasethis distance by taking precaution that adjacent polymer streams do notcome in contact with and cohere to each other. For example, a cellthrough which the streams coaxially pass may be provided to minimize anydisturbance thereof. Ordinarily, the gas between the spinneret and thecoagulating bath and through which the streams of polymer travel is air,although any other gaseous medium that does not adversely affect thefilaments may be used. The temperature of the gas may be regulated;however, the temperature normally present during spinning issatisfactory. For best results the spinning variables should becorrelated so that less than one percent of the solvent based on theWeight of the solution is evaporated into the gaseous medium from theextruded stream.

Although the reason Why the filaments produced by the instant processcan be stretched to a much greater extent between the spinneret and themeans used to Withdraw the coagulatcd filaments is not entirelyelucidated, it is thought that the extrusion of polymer solution througha spinneret positioned above the surface of the coagulating bathprovides a fluid region in each extruded stream of polymer wherein thestreams easily yield to a longitudinally applied force without aseparation of the mass composing the streams. Therefore, considerableattenuation of the streams of polymer can take place prior to the entryof the streams into the coagulating bath. During their brief passagethrough the space above the surface of the coagulating bath and belowthe face of the spiuneret only a small amount of the solvent, if any, isremoved from the extruded streams of polymer with the resuit that littleor no coagulation takes place when the streams are being attenuated.Because of t is high fluidity of the streams of polymer in the Zonebetween the spinneret and coagulating bath, the longitudinal forceapplied to the coagulating filaments to pull same through and out of thecoagulating bath is accepted by the extruded streams of polymer, in themain, in this Zone. Apparently, the coagulating filaments as a resultare passed through the coagulating bath under a minimum tension; thatis, the tension exerted on the coagulating filament would be only thattension required to overcome the viscosity forces within the filamentsand drag forces in the coagulating bath. Under these conditions it isbelieved that isotropic filaments exhibiting only an extremely thinouter skin formation and a reduced susceptibility to skin rupture orfissure to cause undesirable variations in the resulting filaments existin this Zone.

in normal wet spinning a much thicker skin is formed from the verygenesis of filament formation; and the longitudinal force necessary toimpart even a moderate stretch in the filaments undergoing coagulationcan be sufiicient to cause ruptures of the filamentary skin. Thisrupturing also can occur in many instances when the longitudinal forceis sutiicient only to withdraw the filaments from the coagulating bath.It has been observed that when the skin becomes ruptured duringcoagulation, an array of voids forms along the line of skin cleavage.Since the longitudinal forces exerted on the filaments in thecoagulating bath are minimized in accordance with the present invention,the tendency of the surface of the filaments to crack or ruptureaccordingly is reduced, resulting in the production of superiorfilaments.

The coagulating baths suitable for use in the invention normally containa non-solvent such as water, or a mixture of a solvent and a non-solventfor the acrylonitrile polymer. The solvent used in the coagulating bathis preferably the same as the one used in preparing the polymersolution; however, such need not be the case. Although good spinning canbe accomplished while using a coagulating bath composed essentially ofwater, it is preferred that the bath contain 20 percent to percentsolvent. On the basis of available data the temperature range for thecoagulating bath is preferred to be from 40 to +80 C. it is preferredthat the bath contain 6070 percent solvent at the lower bathtemperatures.

The filaments may be given a travel in the coagulating bath, forexample, from 2 to 24 inches or more by employment of the two suitablyspaced guides and with- 1 1 'drawal rolls as illustrated in FIGURE 1.Between the spinneret and the withdrawal rolls, the filaments, asindicated above, are subjected to a stretching operation to attain adesired substantial attenuation thereof.

A second bath is employed following the coagulating bath wherein thefilaments are given an additional stretch in order to increase thestrength, as well as otherwise to improve the physical properties of thefilaments. This improvement results from orientation of the polymermolecules along the filament axis. The second bath may consist simply ofwater, or it may have the same composition as the coagulating bath butat a greater dilution with water. The temperature of the secondary bathis preferably between 50 and 100 C., the highest feasible temperaturebeing preferred. Draw ratios of up to 'or higher may be employed, theamount of stretch applied depends on the properties desired for theyarn. Preferred draw ratios are between 1.5 and 8.0.

Following the passage through the coagulating bath and the stretch bathor baths, the filaments are washed substantially free of solvent ifdesired. This may be accomplished by spraying water on the filamentstraveling around positively driven rolls. The water extracts the solventfrom the filaments as they pass gradually from one end of the rollers tothe other end. Other washing means, of course, can be used. Moreover,the washing can be carried out prior to applying the orientation stretchto the filaments as indicated above.

The next step is important to the proper practice of the presentinvention and consists of subjecting the filaments to sufiicienttemperatures at a low tension or zero tension to permit substantiallycomplete relaxation of the filaments. This may be accomplishedpreferably by continuously passing the filaments through a water bathmaintained at a temperature near or at the boiling point of water bymeans of a thread-advancing device operated at a peripheral speed lessthan the linear velocity at which the filaments are fed to the waterbath. Ordinarily, the filaments may shrink at least percent and up to 40percent of their original length or more. The resulting filaments whichare relaxed in hot or boiling water have higher elongation values ascompared to filaments produced in a comparable manner but without beingpermitted to relax. Surprisingly, the higher elongation values areattained Without a sacrifice of tenacity. More- 'over, it appears thatan inverse relationship exists between the elongation of the resultingfilaments and the temperature at which the filaments are given theorientation stretch. That is to say, for a given orientation stretch,filaments having higher elongation are obtained generally where lowerstretch temperatures are employed. As indicated, the step of relaxing isnot entirely necessary when one follows the low temperature coagulatingbath aspect of the invention.

After the filaments are permitted to freely shrink, they are dried in aconvenient manner. This may be done either under tension or under notension. Preferably, the filaments are dried while in a completelyrelaxed condition so that the filaments are dried and relaxed in oneoperation.

Quite unexpectedly the filaments produced by the present invention afterleaving the relaxation bath have a substantially reduced porosity andhave a smooth, mirror-like surface. Hence, the disadvantages associatedwith drying under tension, such as yellowing of the filaments whensubjected to high local temperatures on the drying drums and likeapparatus used in a tension drying operation, may be avoided and yetproduce filaments that have a luster greater than normal Wet-spunfilaments dried under tens1on.

The examples below are illustrative of the practice of the presentinvention and not limitative thereof. In the examples, all percentagesare given on a weight basis unless otherwise indicated.

12 EXAMPLE I A spinning solution was prepared by dissolving in N,N-dimethylacetamide a blend of (A) a copolymer of 97 percent acrylonitrileand 3 percent vinyl acetate and (B) a copolymer of 50 percentacrylonitrile and 50 percent 2-rnethyl-5-vinylpyridine, said blendcontaining 6 percent vinylpyridine based on the total weight of theblend and having a specific viscosity of 0.12 to give a 26 percentsolids solution. The solution was extruded at 25 C. through a spinneretcontaining holes, each being 0.005 inch in diameter, downwardly throughair for a distance of /2 inch and into a coagulating bath containing 50percent N,N-dimethylacetamide and 50 percent water by volume at 25 C.The bundle of filaments thus formed was led through this bath for adistance of 18 inches and then was removed therefrom at a rate of 30.6feet per minute, the rate of withdrawal being established in relation tothe rate of extrusion so that the filaments are subjected to a drawratio of 0.94 between the spinneret and the means used to withdraw thefilaments from the coagulating bath. Next, the filaments were passedinto a second stretch bath maintained at 100 C. and containingessentially 100 percent water. After traveling a distance of 24 inchesin this second bath, the filaments were withdrawn therefrom at a rate of186 feet per minute so that a stretch of approximately 6.1 times wasimparted to the filaments. Stretch in times, as seen, is the numberresulting from the division of the speed of withdrawal by the speed offeed between two points. Then, the filaments were passed around a pairof spaced rollers 30 to 40 times with a total length of the filamentsaround the rollers at one time being about feet. Water at 50-80 C. wassprayed on the filaments during their travel around said rollers to washthe filaments. Following this washing operation, the filaments weredirected into a relaxing bath containing water at 100 C. with thefilaments being withdrawn therefrom at a speed of 152 feet per minute.Under these conditions the filaments were permitted to shrink 18percent. The filaments next were passed through a bath containing a yarnlubricant and then around a heated drying drum assembly to dry thefilaments. Thereafter, the filaments were crimped, cut into staplelengths, and baled.

The fibers so'produced were lustrous with an excellent resistance toabrasion and had a tenacity of 2.5 grams per denier, an elongation of26.0 percent, and a denier of 3.1.

Additional samples of filaments were prepared in the same manner exceptthat polymer blends having various specific viscosities were used toprepare spinning solutions having various percentages of solids as shownin Table 1 where the yarn properties are also given.

Table 1 Specific Solids, Tenacity, Elongation, viscosity Percentgms/den. Percent It can be seen readily from the above data that widevariations in regard to the specific viscosity of the polymer and to thepercentage of polymer in the spinning solution are permitted in theinstant process.

EXAMPLE II hing solution was extruded-at25 C. through a spinneretcontaining 100 holes, each having a diameter of 0.009 inch, into air fora distance of one inch and into a coagulating bath containing 40 percentN,N-dimethylacetamide and 60 percent water by volume at a temperature of25 C. The bundle of the thus-formed filaments was removed from thecoagulating bath at a rate of 38.4 feet per minute, the rate beingcorrelated to stretch the filaments 6.6 times between the spinneret andthe means used for withdrawing the filaments from the coagulating bath.Then, the filaments were passed into a stretch bath maintained at atemperature of 100 C. and containing Water. The filaments were withdrawnfrom the second bath at a rate of 186 feet per minute so that anadditional stretch of approximately 4.9 times was imparted to thefilaments by employing a thread advancing reel assembly. Water wassprayed on the filaments during their storage on the assembly to washsame. Following this washing operation, the filaments were relaxedthereby causing them to shrink percent in air at room temperature. Ayarn lubricant was applied in a continuous fashion to the filaments, andthen the filaments were dried in a tension-free condition by laying thefilaments onan endless belt conveyor moving through a drying cabinet.The dried filaments were crimped, cut into staple lengths, and baled.The fibers so-produced were lustrous with an excellent resistance toabrasion and had a tenacity of 2.7 grams per denier and an elongation of16.4 percent.

EXAMPLE III A spinning solution was prepared in N,N-dimethyl acetamidecontaining 18 percent polymer based on the weight of the solution. Thepolymer employed was the polymer blend used in Example I and had aspecific viscosity of 0.16. Samples of the spinning solution wereextruded at 25 C., 120 C., and 180 C., respectively, through a spinneretcontaining 40 holes, each having a diameter of 0.005 inch into air for adistance of inch and then into a coagulating bath containing 40 percentN,N-dimethylacetamide and 60 percent water by weight and maintained at atemperature of 28 C. The filaments were processed then into staplefibers in the manner described in Example II. However, the filamentswere given a jet stretch of 1.3 times and an orientation stretch of 4.9times in the second bath. The fibers so-produced were highly lustrouswith an excellent resistance to abrasion. The textile data of thesespinnings are tabulated below in Table 2.

Table 2 Solution Tenacity, Elongation, temperagins/den. Percent ture, C.

EXAMPLE IV T able 3 Spinncret coagulating bath Sample Diameter,Solvent/Water, Ma imum Holes inches percent C. stretch,

times It can be noted from the above data that a significant nma emaximunsttet bi alue ccurr d en he solvent content of the coagulatingbath was above 50 percent. Stretches above 10 times were obtainable.Unlike in normal wet spinning where the opposite relationship holds, themaximum. jet stretch of the subject invention decreased with increasingamounts of water in the coagulating bath and increased with decreasingamounts of water in the coagulating bath.

EXAMPLE V A spinning solution was prepared in N,N-dimethylacetamidecontaining 18 percent polymer of the type employed above in Example Ibut having a specific viscosity of 0.25. The spinning solution wasextruded at 25 C. through a spinneret containing 40 holes, each having adiameter of 0.005 inch, into air for a distance of /2 inch and then intoa coagulating bath containing 10 percent N,N-ditnethylacetamide and 90percent water by volume at a temperature of 27 C. The thus-formedfilaments were stretched 1.3 times and then passed through a second bathcontaining water at 100 C. During their travel through the second baththe filaments were stretched 5.0 times. The filaments were washed andthen dried While in a tension-free condition.

Additional spinnings were carried out at temperatures of 90 C., 80 C.,and C. in the second stretch bath. At these various temperatures thefilaments were stretched to different extents as indicated from Table 4.

Table 4 Second Stretch Percent bath, in second shrink- Tenacity, Elonga-Sample temp., bath, age dur- Denier gins] tion,

0. times ing reden. percent latation From the data above it is seen thatthe percent elongation increased for a given stretch in the second bathas the temperature in the bath was decreased without an appreciablesacrifice in tenacity.

For comparison purposes the spinneret was immersed in the coagulatingbath and the same spinning solution was spun into filaments under likeconditions. It was found that a second bath temperature of C. or abovewas required to attain stretches of up to 4 to 5 times.

15 Furthermore, stretches greater than times were impossible; below thistemperature the maximum stretch obtainable was even less than 4.

Hence, it is seen that in the present method the filaments can be givenan orientation stretch in the second bath over a relatively widetemperature range without sacrifice of yarn properties. From practicalconsiderations this wide latitude of temperature assumes considerablesignificance, since there is no necessity of rigid temperature controland since more energy is required to maintain the bath at the hightemperature required in regular wet spinning.

EXAMPLE VI Samples Q, R, and T above in Example IV were washed withwater and permitted to relax and not to relax in an aqueous bath. Theresulting filaments were dried on heated rotating rolls and theirphysical properties determined. These results are given in Table 5below.

These data show that the relaxed samples had a significantly higherelongation as compared with the unrelaxed samples, but unexpectedlytenacities remained substantially unchanged. The fibers having thegreater elongation and produced by employing the relaxation step hadconsiderably less breaks on the card when processed on the cotton systemthan the fibers with the low elongations.

EXAMPLE VII The effect of various orientation stretches in the secondbath and continuous relaxation on the physical properties of the formedfilaments in regard to tenacity and elongation was studied whileemploying a coagulating bath having a relatively low temperature.

A spinning solution was prepared in N,N-dimethylacetamide containing 18percent polymer based on the weight of the solution. The polymeremployed was the polymer blend used in Example 1 above and had aspecific viscosity of 0.25. Samples of the spinning solution wereextruded through a spinneret containing 100 holes, each having adiameter of 0.0035 inch into air for a distance of /3 inch. The extrudedstreams of polymer were directed into a coagulating bath containing 70percent N,N-dimethylacetamide and 30 percent water by volume. Thecoagulating bath was maintained at 5 C: 1 The extruded streams weredirected through this bath for 24 inches; the bundle of filamentsthus-formed was then removed therefrom at a rate of 22 to 44 feet perminute, the rate of withdrawal being established in relation to the rateof extrusion so that the filaments were subjected to a draw ratio of 0.8between the spinneret and the means used to withdraw the filaments fromthe coagulating bath. Next, the filaments were passed through a waterbath at 60 C. so as to remove residual solvent from the filaments.

'Ihe filaments were next directed through a water bath at about 100 C.and stretched therein a predetermined extent. Various stretches weregiven the samples at this stage. Some of the samples were directed intoa relaxing bath containing water at about 100 C. and other samples werenot. The filaments were collected on cones and dried in air. Thetenacity and elongation were measured on the filaments. These resultsare given in Table 6 below.

Table 6 Percent Stretch in shrinkage Tenacity, Elongation, Sample secondduring Denier gmsJden. percent bath, times relaxation 6.0 None 2. 8 4.513 6.0 15 3. 2 8. 9 26 5.0 None 2.8 4.1 14 5.0 15 3. 2 3.4 25 4.0 None2.8 3.7 16 4.0 15 3.2 3.2 27 3.0 None 2. 7 3.1 18 3.0 15 3.1 2.8 30

Thus, from the above data, it is indicated that satisfactory textileproperties are obtained by employing relatively low coagulating bathtemperatures even though the yarn is not permitted to relax after beingstretched to induce molecular orientation therein.

EXAMPLE vnr' Additional spinnings were carried out following theprocedure outlined above in Example VII. The acrylonitrile polymer inthis instance was a binary copelymer of 94 weight percent acrylonitrileand 6 weight percent vinyl acetate. The effect of various orientationstretches in the second bath and continuous relaxation on the physicalproperties of the formed filaments in regard to tenacity and elongationwhile employing coagulating baths having various relatively lowtemperatures as set forth in Table 7 below was demonstrated. The finalfilaments had a denier of about 3.1 when permitted to relax and a denierof about 2.7 when not so permitted.

Table 7 Qoagulat- Stretch in Percent Elonga- Sample ting bath secondshrinkage Tenacity, tion, permp., 0 bath, during gmsJden. cent timesrelaxation -10 6.0 None 4. 1 18 -l0 6.0 16 4. 5 25 -l0 4.0 None 3.3 17-10 4. 0 16 3. 6 24 -l0 2.0 None 2. 9 19 -10 2. 0 16 2. 8 27 0 6. 0 None4.0 18

0 4. 0 None 3. 6 20 0 2.0 None 2. 8 21 10 0.0 None 4.0 18

10 4. 0 None 3. 3 16 10 2.0 None 2. 7 27 The following indications maybe read into the above data: A gradual reduction in bath temperatureresults in a corresponding increase in tenacity. Furthermore, a highertenacity is obtained when greater stretches are imparted to thefilaments in the second bath. In addition, the yarnnot permitted torelax has physical properties comparable to the yarn permitted to relax.Hence, while relaxation is important to obtain optimum properties whenrelatively high temperature coagulating baths are employed, the step ofrelaxing may be omitted with low temperature coagulating bath spinningwithout a substantial sacrifice of properties.

EXAMPLE IX The effect of various bath temperatures on tenacity,elongation and abrasion resistance was studied, the value for abrasionresistance being tabulated as cycles to break at a gram load.

Spinning solutions were prepared in N,N-dimethylacetamide containing 18percent polymer based on the weight of the solution. In one instance thepolymer employed was the polymer blend used in Example I; in the secondinstance, the polymer was a copolymer of 94 weight per- 17 centacrylonitrile and 6 weight percent vinyl acetate. These samples in thedata which follow in Table 8 are identified as A and B, respectively.Samples of the spinning solution were extruded into filaments by thespinning technique described in Example VII. The coagulating bath wascomposed of 70 percent N,N-dimethylacetamide and 30 percent water andwas maintained at the temperature indicated in Table 8. The filamentswere collected without permitting same to relax.

The study indicates a general improvement in abrasion resistance ascoagulating bath temperature is decreased. The abrasion resistance wasmeasured by using the simple laboratory device disclosed in FIGURE 7. Asseen, the device comprises a synchronous motor 80 adapted to drive wheel81. Near the periphery of Wheel 81 is a rotatably mounted peg 82. Oneend of the yarn 83 which is to be tested for abrasion resistance isattached to the peg as shown.- The yarn is threaded around pulley 84 andaround one side of a stationary horizontally disposed pin 85. Tocomplete the threading-in the yarn is passed around pulley 86 with aweight 87 being tied to the other end of the yarn. The pin 85 is a roundlong rigid metal wire having a smooth surface and a diameter of about0.006 inch. During the test the motor is operated .at 60 revolutions perminute and the revolutions are counted until the yarn breaks. The denierof the yarn in each case was the same. The weight, as indicated above,in the test was 100 grams.

EXAMPLE X The abrasion resistance when the yarn is dry and when I 80percent by weight acrylonitrile and up to 20 percent fof anothermono-olenific monomer.

the yarn is saturated with water was studied.

' A spinning solution was prepared by dissolving a co polymer of94-weight percent acrylonitrile and 6 weight percent vinyl acetate inN,N-dimethylacetamide in an amount that the solution contained. 25percent polymer. The solution was extruded into a short air gap and spuninto acrylic filaments as described in Example VII. However, thecoagulating bath had a composition of 70 percent N,N-dimethylacetamideand 30 percent water and was maintained at a temperature of -l C. Theorientation stretch was 5.5 times and the filament yarn before dryingand collecting was not permitted to relax. The resulting yarn wasuptwisted to a twist of 3-5 turns per inch and knitted into a narrowtape 14 ends wide on a tricot knitting machine. The resulting tape wasthen tested on the Stoll Abrader until failure occurred. To break theknitted tape by the use of the Stoll Abrader, 5.06 cycles were requiredwhen wet, and 365 cycles were required to break the tape when dry.

In an additional spinning the polymer solution was extruded through ashort air gap and into a coagulating bath composed of 30 percentN,N-dimethylacetamide and 70 percent water and maintained at atemperature of -5 C. The orientation stretch was 5.5 times and thefilament yarn before drying and collecting was not permitted to relax.The yarn was knitted into tricot tape as described above and tested onthe Stoll Abrader. To break the wet tape required 635 cycles on theStoll Abrader whereas dry tape broke at 414 cycles.

The present invention makes possible the production of acrylonitrilepolymer filamentsthat have an optimum balance of longitudinal andlateral properties and that are eminently suitable for use in thetextile art. The filaments have increased elongation realized withoutsacrifice of tenacity, the higher elongation enabling the filament to betougher and to be able to absorb more energy without breakage. Inaddition, the speed at which the filaments may be produced is notablyhigh. Moreover, filaments that are substantially free from voids andhave a high lustrous appearance can be produced. It is not necessaryaccording to the present invention to dry the filaments under tension inorder to produce a satisfactory dense fiber structure. Also, the presentprocess lends itself readily to employment on a commercial scale withoutsubstantial modification of conventional spinning equipment. Numerousother advantages of the present invention will be apparent to thoseskilled in the art.

Any departure from the description herein that conforms to the presentinvention is intended to be included within the scope of the claims.

This application is a continuation-in-part application of copendingapplication Serial No. 315, filed January 4, 1960, the latterapplication being a continuation-impart application of applicationSerial No. 783,226, filed December 29, 1958 (now abandoned).

What is claimed is:

1. A process for producing a shaped article from an acrylonitrilepolymer which comprises the steps of preparing a solution containingsaid polymer, extruding the resulting solution into a stream by forcingsaid solution through a shaped orifice into a gaseous evaporative mediumin which only a small amount of the solvent used in the preparation ofsaid solution is evaporated from the stream as a gas, directing saidstream through saidmedium for a short distance and into a coagulatingbath comprising a liquid that is a precipitant for the polymer secondliquid and stretching same in the presenceof said second liquid toorient the polymer molecules thereof,

and then permitting the article to relax and thereby, to shrink I 2. Theprocess as defined in claim 1 wherein the acrylonitrile polymer is acopolymer containing at least 3. The process as defined in claim 1wherein the mer is polyacrylonitrile. 1 1 i 4. The process as defined inclaim 2 wherein the monoolefinic monomer is vinyl acetate.

5. The process as defined in claim 1 wherein the acrylonitrile polymeris a blend of a copolymer of to 99 percent acrylonitrile and 20 to 1percent of another mono-olefinic monomer and a copolymer of 10 to 70percent acrylonitrile and to 30 percent of a vinylsubstituted tertiaryheterocyclic amine, said blend having an overall vinyl-substitutedtertiary heterocyclic amine content of 2 to 10 percent, based on theweight of the blend.

6. A process for producing a filament from an acrylonitrile polymer'which comprises the steps of preparing a solution containing saidpolymer by dissolving a copolymer of at least 80 percent by weight ofacrylonitrile and up to 20 percent of another mono-olefinic monomer in asolvent therefor, extruding the resulting solution into a stream byforcing said solution through an orifice of a spinneret whose face isdisposed in a gaseous evaporative medium, directing said stream throughsaid medium and into a coagulating bath comprised of water and thesolvent after the stream has passed through said medium for a shortdistance and after a small amount of the solvent has evaporated from thestream as a gas, withdrawing the thus-formed filament from thecoagulating bath,

stretching the filament between the point of extrusion and point ofwithdrawal to attenuate same a considerable extent, passing the filamentthrough a second liquid and stretching same in the presence of saidsecond liquid to 'orient the polymer molecules thereof, washing saidfilament by passing the same through a water bath, then subjecting thefilament in water to a sufficient temperature at a low tension to permitthe filament to relax substantially completely and thereby to shrink atleast to 40 percent in a substantially tension-tree condition whilebeing dried.

7. A process for producing a filament from an acrylonitrile polymerwhich comprises the steps of preparing a solution containing saidpolymer by dissolving a copolymer of at least 80 percent by weightacrylonitrile and up to percent of another mono-olefinic monomer in asolvent therefor, extruding the resulting solution into a stream byforcing said solution through an orifice in a spinneret horizontallydisposed in air, directing said stream through said air and into acoagulating bath comprised of water and the solvent after the stream haspassed substantially vertically downward through the air and after asmall amount of solvent has evaporated from the stream as a gas,withdrawing the thus-formed filament from the coagulating bath,stretching the filament between the point of extrusion and point ofwithdrawal by at least three times but short of the breaking point ofthe 'olefinic monomer is vinyl acetate.

9. The process as defined in claim 7 wherein the acrylonitrile polymeris a blend of a copolymer of 80 to 99 ercent acrylonitrile and 20 to 1percent of another monoolefinic monomer and a copolymer of 10 to 70percent 'acrylonitrile and 90 to 30 percent of a vinyl-substitutedtertiary heterocyclic amine, said blend having an overallvinyl-substituted tertiary heterocyclic amine content of 2 to 10percent, based on the weight of the blend.

10. A process for producing a filament from an acrylonitrile polymerwhich comprises the steps of preparing a solution containing saidpolymer by dissolving a copolymer of at least 80 percent by weightacrylonitrile and upto 20 percent of another mono-olefinic monomer inN,N.-dimethylacetamide, extruding the resulting solution into a streamby forcing said solution through a shaped orifice in air, directing saidstream through air and into a coagulating bath comprising a liquid thatis a precipitant for the polymer and an'extractant for N,N-dimethylacetamide after the stream has passed a short distance throughthe air and after only a small amount of N,N-dimethylacetamide hasevaporated from the stream as a gas, withdrawing the thus-formedfilament from the coagulating bath, stretching the filament between thepoint of extrusion and point of withdrawal to attenuate same aconsiderable extent, passing the filament through a second liquid andstretching same in the presence of said second liquid to orient thepolymer molecules thereof, then relaxing the filament substantiallycompletely to shrink same, and thereafter drying the filament.

11. A process for producing a filament'from an acrylonitrile polymerwhich comprises the steps of preparing a solution containing saidpolymer by dissolving a copolymer of at least percent by weightacrylonitrile and up to 20 percent of another mono-olefinic monomer inN,N-dimethylacetamide, extruding the resulting solution at a temperatureof 20 to 180 C. into a stream by forcing said solution through anorifice in a spinneret whose face is horizontally disposed in air,directing said stream through air and into a coagulating bath composedof to 20 percent non-solvent for the polymer and 0 to 80 percentN,N-dimethylacetamide after the stream has vertically passed downwardthrough the air for a distance of A5 to 1 /2 inches and after at mostone percent of N,N-dimethylacetamide has evaporated from the stream as agas, withdrawing the thus-formed filament from the coagulating bath,stretching the filament just short of its breaking point between thepoint of extrusion and point of withdrawal, passing the filament througha second liquid and stretching same in the presence of said secondliquid to orient the polymer molecules thereof, washing the filament bycontacting it With water, then subjecting the filament in water to-asufiicient temperature at a low tension to permit the filament to relaxsubstantially completely and thereby to shrink at least 15 to 40percent,

and thereafter drying the filament in a substantially tension-freecondition.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR PRODUCING A SHAPED ARTICLE FROM AN ACRYLONITRILEPOLYMER WHICH COMPRISES THE STEPS OF PREPARING A SOLUTION CONTAININGSAID POLYMER, EXTRUDING THE RESULTING SOLUTION INTO A STREAM BY FORCINGSAID SOLUTION THROUGH A SHAPED ORIFICE INTO A GASEOUS EVAPORTIVE MEDIUMIN WHICH ONLY A SMALL AMOUNT OF THE SOLVENT USED IN THE PREPARATION OFSAID SOLUTION IS EVAPORATED FROM THE STREAM AS A GAS, DIRECTING SAIDSTREAM THROUGH SAID MEDIUM FOR A SHORT DISTANCE AND INTO A COAGULATINGBATH COMPRISING A LIQUID THAT IS A PRECIPITANT FOR THE POLYMER AND ANEXTRACTANT FOR THE SOLVENT, WITHDRAWING THE THUSFORMED ARTICLE FROM SAIDCOAGULATING BATH, STRETCHING SAID ARTICLE BETWEEN THE POINT OF EXTRUSIONAND POINT OF WITHDRAWAL TO ATTENUATE SAME, PASSING THE ARTICLE THROUGH ADSECOND LIQUID AND STRETCHING SAME IN THE PRESENCE OF SAID SECOND LIQUIDTO ORIENT THE POLYMER MOLECULES THEREOF, AND THEN PERMITTING THE ARTICLETO RELAX AND THEREBY TO SHRINK.